UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 

•Illllllllllll 

AA    001  185732    3 


CIRCULAR  No.  21. 

United  States  Department  of  Agriculture, 

OFFICE    OF    ROAD    INQUIRY. 

METHODS  OF  CONSTRUCTING  MACADAMIZED  ROADS. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

OFFICE  OF  ROAD  INQUIRY, 

\Vaxli iiiyton,  D.  C.,  June  6,  18')«i. 

SIR  :  The  Bureau  of  Highways  of  the  State  of  California  having  requested  Her 
Majesty's  Office  of  Works  to  ' '  acquaint  them  with  the  methods  employed  in  Eng- 
land in  the  matter  of  highway  improvement,"  the  Marquis  of  Salisbury  trans- 
mitted the  following  report  prepared  by  the  chief  engineering  inspector  of  the 
local  government  board  to  the  ambassador  of  the  United  States,  who  forwarded 
it  to  the  Secretary  of  State  with  the  observation  that,  "  in  view  of  the  general 
interest  felt  in  this  subject,  I  venture  to  suggest  that  it  would  appear  very  expe- 
dient if  the  report  now  transmitted  could  be  printed  for  public  information." 

The  Office  of  Road  Inquiry  has  obtained  permission  of  the  California  Biireau 
of  Highways  to  make  any  desired  use  of  this  report,  and,  in  view  of  the  many 
valuable  suggestions  contained  therein,  I  would  recommend  its  publication  as 
Circular  No.  21  of  this  office. 

Very  respectfully. 

ROY  STONE, 

Hon.  J.  STERLING  MORTON,  Special  Agent  and  Engineer. 

Secretary  o/'  .\ijrifulturc. 


Extract  from  a  Report  Prepared  l»y  the  Chief  Engineering  Inspector  of  the 
Local  Government  Board. 

INTRODUCTION. 

Our  country  roads  have  not  been  made  with  any  particular  kind  of  material, 
or  in  any  particular  way,  but  have  grown  up  just  as  the  exigencies  of  trade  or 
traffic  demanded  and  according  to  no  set  rules  or  principles.  They  consequently 
present  the  greatest  differences.  While  some  are  as  wide  as  the  widest  streets  in 
towns,  others  are  mere  lanes  where  two  carriages  meeting  can  not  pass  each  other. 

In  England  it  can  hardly  be  considered  that  there  was  any  art  or  science  in 
roadmaking  until  the  early  part  of  the  present  century,  and  it  is  almost  impossible 
to  enter  into  any  discussion  of  the  technical  points  in  connection  with  the  forma- 
tion and  maintenance  of  roads  without  referring  to  the  maxims  and  practice  of 
the  great  pioneer  in  this  branch  of  civil  engineering  whose  genius  is  not  only 
universally  acknowledged,  but  has  even  stamped  itself  on  the  European  languages. 

After  a  considerable  experience  of  roadmaking  in  Scotland  and  elsewhere,  John 
Loudon  Macadam  appears  to  have  settled  some  time  before  1820  at  Bristol,  where 
he  was  made  a  magistrate  of  the  county  and  appointed  general  siirveyor  of  the 
roads  in  the  district.  When  he  took  charge  of  these  roads  it  is  admitted  that  they 
were  more  or  less  in  a  deplorable  condition,  but  in  a  very  short  time  after  they 
passed  under  his  charge  they  were  transformed  as  if  by  the  wand  of  the  magician 
into  such  an  efficient  state  that  all  classes  bore  the  amplest  testimony  to  his  suc- 
cess, especially  that  class  who  had  the  best  opportunities  of  judging  and  whose 


interests  were  pecuniarily  affected  by  the  state  of  the  roads — the  great  coach  pro- 
prietors before  railways  were  introduced  into  the  country.  His  experience,  more- 
over, was  not  confined  to  any  single  county,  but  he  was  consulted  by  authorities 
in  all  parts  of  England,  so  that  his  knowledge  of  the  subject,  both  in  respect  of 
its  technical  details  and  its  actual  practice,  was  such  as  no  one  else  possessed. 

His  experience,  too,  was  of  that  highest  kind  which  is  derived  from  the  actual 
carrying  out  of  works  over  a  wide  field  of  action.  He  constructed  roads  on  plains 
and  over  hills,  on  hard  grounds  and  on  soft,  over  rocks  and  across  swamps,  with 
granite,  with  whinstone,  with  flints,  with  limestone,  with  gravel,  and  with  every 
kind  of  available  materials,  and  he  appears  to  have  carefully  observed  the  results 
of  his  labors  in  each  instance.  These  results  were  obtained,  moreover,  not  with 
an  increased  expenditure,  but  with  an  actual  saving.  His  roads  cost  less  both 
to  form  and  to  maintain. 

Just  as  no  work  on  roads  is  ever  written  without  an  explanation  of  Macadam's 
principles,  so  it  is  equally  necessary  in  this  paper  to  refer  from  time  to  time  to 
those  principles,  and  to  discuss  them  in  connection  with  the  more  extended 
knowledge  and  better  appliances  of  the  present  day. 

WIDTH  OF  ROADS. 

There  is  nothing  like  uniformity  in  the  width  of  the  county  roads  in  the  King- 
dom, some  of  which  are  as  wide  as  80  feet,  while  others  are  only  one  tenth  of 
that  width,  i.  e. ,  so  narrow  that  even  two  carts  can  not  pass  each  other  on  them. 
The  average  width,  however,  may  approximately  be  taken  at  from  15  to  30  feet 
for  the  metaled  portions.  There  is  also  no  uniformity  as  to  the  footways.  On 
some  roads  there  are  no  footpaths  on  the  sides  at  all ;  on  others  there  is  a  foot- 
way on  one  side  only ;  and  on  others,  on  both  sides.  Moreover,  these  paths, 
which  are  usually  of  gravel  and  raised  from  6  to  12  inches,  but  in  some  places 
much  more,  above  the  metaled  portions  of  the  road,  and  which  generally  slope 
toward  the  carriage  ways,  differ  much  in  width. 

In  some  places  also  there  is  a  strip  of  greensward  on  the  side  of  the  carriage- 
way which  is  used  by  equestrians,  sheep,  and  cattle. 

These  same  observations  apply  also  to  all  other  roads  in  the  country.  There  is 
no  more  uniformity  to  be  found  in  them  than  in  the  coiinty  roads.  They  vary 
in  width  exceedingly,  being  in  some  places  as  wide  as  first-class  county  roads, 
and  in  others  dwindling  down  to  exceedingly  narrow  lanes.  These  roads  too 
have  in  some  places  footpaths,  and  in  others  none. 

With  regard  to  the  proper  width  that  should  be  given  to  roads,  it  is  manifest 
that  this  should  depend  on  the  object  to  be  served  by  the  particular  road.  Main 
roads,  which  are  the  principal  means  of  communication  between  large  centers  of 
population,  must  not  only  be  wider  than  mere  country  roads,  which  run  from 
village  to  village,  or  are  only  required  for  the  purposes  of  farmers,  but  must  be 
wider  near  towns  than  at  a  distance  from  them. 

Macadam  thought  that  ' '  roads  near  great  towns  ought  not  to  be  less  than  30 
or  40  feet  wide,  but  at  a  distance  from  great  towns  it  would  be  a  waste  of  land 
to  make  them  so  wide." 

No  hard  and  fast  rule  can  be  made  unless  it  is  that  every  road  which  is  intended 
for  carriage  traffic  should  be  sufficiently  wide  to  admit  of  two  carriages  passing 
each  other  easily,  otherwise  the  greatest  inconvenience  must  be  caused.  The 
surveyor  in  designing  new  roads  must  be  guided  by  his  knowledge  of  the  traffic 
of  the  district  and  must  regulate  their  widths  accordingly.  For  country  roads 
the  widths  should  be  somewhat  more  than  twice  the  width  of  the  vehicles  and 
carts  used  in  the  particular  country  or  locality,  so  as  to  allow  the  wheels  to  pass 
each  other  easily,  and  for  ordinary  main  roads  twice  this  width  would  answer 
every  reasonable  purpose.  If  a  road  is  made  less  than  the  width  of  two  carts, 
it  should  widen  out  for  a  short  length,  at  regular  distances  apart,  to  a  little  more 
than  the  width  of  two  carts,  so  as  to  admit  of  carts  passing  each  other  at  these 
refuges;  but  this  is  at  best  an  imperfect  arrangement,  as  the  drivers  do  not  see 
each  other  till  they  suddenly  meet,  when  one  must  go  back  to  the  nearest  refuge 
to  let  the  other  pass. 

It  should  be  borne  in  mind  that  the  cost  of  maintaining  a  well-formed  road  is 
not  in  proportion  to  its  width,  but  more  in  proportion  to  the  traffic  passing  over 
it,  so  that  in  laying  down  a  new  road  it  is  better  to  make  it  too  wide  than  too 
narrow.  Greater  width  affords  greater  convenience  to  traffic,  and  the  road  is 
not  so  often  under  repair.  A  narrower  road,  for  the  same  amount  of  traffic,  is 
of  tener  under  repair  and  wears  out  both  horses  and  carts  much  sooner.  This  is 
particularly  the  case  where  the  road  is  formed  with  inferior  material. 


GRADIENTS. 

Inasmuch  as  the  roads  everywhere  have  been  constructed  as  they  have  been 
required  in  times  past,  and  without  the  technical  knowledge  of  the  present  day, 
the  gradients  usually  were  made  to  conform  in  great  part  to  the  character  of  the 
country  over  which  they  passed,  and  where  obstacles  such  as  hills  were  met  with, 
the  roads  were  generally  carried  over  them  without  any  ruling  gradient  having 
been  adopted.  Some  of  the  old  roads  with  very  steep  gradients  have  been,  or  are 
being,  gradually  altered  from  time  to  time,  but  it  would  be  very  desirable  to 
improve  many  others  in  the  same  way.  Sir  John  Macneil  advocated  a  ruling 
gradient  of  not  less  than  1  in  40 ;  Professor  Mahan,  1  in  33 ;  and  Telford,  about  1 
in  30.  If  a  ruling  gradient  not  steeper  than  1  in  30  could  be  generally  adopted 
throughoiit  the  country,  except  for  very  short  distances,  in  cases  where  the  cost 
would  be  out  of  all  proportion  to  the  advantage  gained,  an  immense  benefit  would 
be  derived  by  the  public. 

The  limit  of  the  longitudinal  gradient  for  macadamized  roads  as  to  steepness 
should  not  exceed  about  1  in  20,  and  as  to  flatness,  about  1  in  100.  A  perfectly 
flat  road  is  generally  objectionable,  in  consequence  of  the  difficulty  of  draining 
it  properly,  but  the  objection  does  not  hold  good  if  the  road  is  raised  above  the 
surface  of  the  country,  and  its  drainage  can  be  effected  properly. 

Although  the  first  cost  of  a  road  with  a  good  gradient  may  be  greater  than  that 
with  a  steeper  one,  the  subsequent  charge  of  maintenance  is  in  favor  of  the  for- 
mer, as  flat  roads  with  the  same  amount  of  traffic  do  not  cost  nearly  so  much  as 
steep  ones. 

CROSS  SECTION. 

The  gradient  from  the  middle  of  the  road  to  the  side  is  a  technical  point  of  the 
first  importance,  and,  as  usual,  it  was  Macadam  who  really  reasoned  out  the  prin- 
ciple which  should  guide  the  surveyor.  He  said: 

'  'A  road  should  be  as  flat  as  possible  with  regard  to  allowing  the  water  to  run 
off  at  all,  because  a  carriage  ought  to  stand  upright  in  traveling  as  much  as  pos- 
sible. I  have  generally  made  roads  3  inches  higher  in  the  center  than  I  have  at 
the  sides  when  they  are  18  feet  wide.  If  the  road  be  well  made  the  water  will 
run  off  very  easily  in  such  a  slope. 

"When  a  road  is  made  flat,  people  will  not  follow  the  middle  of  it  as  they  do 
when  it  is  made  extremely  convex.  Travelers  generally  follow  the  track  in  the 
middle,  which  is  the  only  place  where  the  carriage  can  run  upright,  by  which 
means  three  furrows  are  made  by  the  horses  and  the  wheels,  and  the  water  con- 
tinually stands  there ;  and  I  think  more  water  actually  stands  upon  a  very  convex 
road  than  on  one  which  is  reasonably  flat." 

The  cross  slope,  therefore,  recommended  by  Macadam,  viz :  3  inches  in  a  road 
18  feet  wide,  would  be  1  in  36.  For  a  road  30  feet  wide  Macadam  also  recom- 
mended a  fall  of  only  3  inches  from  the  center  to  the  sides.  This  would  be  a  gra- 
dient of  only  1  in  60.  There  is  no  explanation  of  this  apparent  discrepancy  in  his 
practice,  but  he  may  have  considered  that  a  wider  road  might  have  a  flatter  cross 
section  because  it  has  generally  a  smoother  surface.  Another  engineer,  John 
Walker,  who  lived  in  Macadam's  time,  advocated  that  the  surface  of  the  road 
"should  be  made  with  a  very  gentle  curve  in  its  cross  section,  just  sufficient  to 
permit  the  water  to  pass  from  the  center  toward  the  sides.  The  declivity  may 
increase  toward  the  sides,  and  the  general  section  form  a  very  flat  ellipsis,  so  that 
the  side  should  (upon  a  road  of  about  30  feet  in  width)  be  9  inches  below  the  sur 
face  in  the  middle."  Such  a  slope  would  practically  be  equivalent  to  1  in  20,  and 
would  be  much  steeper  than  the  best  authorities  in  the  present  day  recommend. 

The  slopes  actually  given  to  the  roads  in  the  country  follow  no  rule.  Some  of 
the  roads  are  almost  flat,  while  others  are  very  convex. 

There  is  one  serious  disadvantage  in  giving  the  surface  of  the  road  an  elliptical 
form,  which  is  that  the  center  portion  has  one  slope  while  the  sides  have  another. 
This  is  most  inconvenient  to  traffic  and  actually  dangerous  to  carriages  moving 
at  a  great  pace.  The  sudden  change  from  one  slope  to  another  is  very  apt  to 
overturn  the  vehicle,  particularly  if  there  should  happen  to  be  any  loose  stones 
lying  on  the  surface.  It  is  somewhat  illogical,  moreover,  to  advocate  such  a 
form  for  a  road,  as,  if  the  flatter  portion  of  the  surface  has  a  sufficient  slope,  the 
remaining  portion  must  have  too  steep  a  one ;  or,  again,  if  the  sides  have  a  proper 
slope,  the  middle  of  the  road  must  be  too  flat.  Extreme  steepness  at  the  sides 
practically  narrows  a  road  for  use,  and  also  tends  to  the  more  rapid  destruction 
of  these  portions  of  the  highway. 


The  slope  should  be  regulated  with  the  following  objects  in  view : 

The  rain  falling  should  be  able  to  escape  readily  to  the  sides,  but  not  with  such 

a  velocity  as  to  create  ruts  on  the  surface. 

The  road  should  be  as  flat  as  possible  consistent  with  the  first  principle,  so  as 

to  offer  no  inducement  to  vehicles  to  keep  to  any  particular  part  of  it,  and  thus 

to  wear  that  part  out. 

FOUNDATION. 

Macadam  thought  a  foundation  of  large  stones  or  other  suitable  material  for  the 
metaling  to  rest  on  was  not  only  unnecessary,  but  that  it  was  positively  injurious. 

A  thickness  of  10  inches  of  metaling  well  consolidated  in  layers  of  about  3 
inches  or  so,  and  placed  on  a  dry  subsoil  (a  sine  qua  non  with  him),  was  in  his 
opinion  sufficient  to  carry  the  heaviest  traffic  even  over  soft  ground.  He  never 
used  large  stones  for  a  foundation  in  his  practice  of  roadmaking.  He  said : 

"The  roads  can  never  be  rendered  perfectly  secure  until  the  following  princi- 
ples be  fully  understood,  admitted,  and  acted  upon,  viz :  that  it  is  the  native  soil 
which  really  supports  the  weight  of  traffic ;  that  while  it  is  preserved  in  a  dry 
state  it  will  carry  any  weight  without  sinking,  and  that  it  does  in  fact  carry  the 
road  and  the  carriages  also ;  that  this  native  soil  must  be  previously  made  quite 
dry,  and  a  covering  impenetrable  to  rain  must  then  be  placed  over  it  in  that  dry 
state ;  that  the  thickness  of  a  road  should  only  be  regulated  by  the  quantity  of 
material  necessary  to  form  such  impervious  covering,  and  never  by  any  reference 
to  its  own  power  of  carrying  weight. 

"The  erroneous  opinion  so  long  acted  upon  and  so  tenaciously  adhered  to,  that 
by  placing  a  large  quantity  of  stone  under  the  roads  a  remedy  will  be  found  for 
the  sinking  into  wet  clay  or  other  soft  soil,  or,  in  other  words,  that  a  road  may 
be  made  sufficiently  strong  artificially  to  carry  heavy  carriages  though  the  sub- 
soil be  in  a  wet  state,  and  by  such  means  to  avert  the  inconvenience  of  the  nat- 
ural soil  receiving  water  from  rain  or  other  causes,  has  produced  most  of  the 
defects  of  the  roads  of  Great  Britain. 

"At  one  time  I  had  formed  the  opinion  that  this  practice  was  only  a  useless 
expense,  but  experience  has  convinced  me  that  it  is  likewise  positively  injurious. " 

The  following  evidence  given  by  him  before  a  Parliamentary  committee  shows 
still  more  clearly  what  views  he  held  on  the  subject: 

"I  should  think  that  10  inches  of  well-consolidated  material  is  equal  to  carry 
anything." 

Query:  "That  is,  provided  the  substratum  is  sound?" 

Answer :  ' '  No,  I  should  not  care  whether  the  substratum  was  soft  or  hard ;  I 
should  rather  prefer  a  soft  one  to  a  hard  one." 

Query:  "You  don't  mean  you  would  prefer  a  bog?" 

Answer:  "If  it  was  not  such  a  bog  as  would  not  allow  a  man  to  walk  over  I 
should  prefer  it."  *  *  *  "I  think  when  a  road  is  placed  on  a  hard  sub- 
stratum, such  as  rock,  the  road  wears  much  sooner  than  when  placed  on  a  soft 
substratum." 

Query :  ' '  But  must  not  the  draught  of  a  carriage  be  much  greater  on  a  road 
which  has  a  very  soft  foundation  than  over  one  which  is  of  a  rocky  foundation? " 

Answer :  "I  think  the  difference  would  be  very  little  indeed,  because  the  yield 
of  a  good  road  on  a  soft  foundation  is  not  perceptible." 

Macadam  thought  that  a  road  lasted  much  longer  over  a  soft  than  over  a  hard 
substratum,  and  independent  evidence  was  given  before  Parliament  to  prove  this 
in  respect  of  a  road  between  Bristol  and  Bridgewater,  part  of  which  ran  over  a 
morass,  and  part  over  a  rocky  foundation.  It  was  contended  by  Macadam  that 
the  unyielding  rock  caused  the  road  to  wear  away  much  faster.  This  seems, 
however,  to  be  directly  opposed  to  the  experience  of  most  engineers  whose  prac- 
tice it  usually  is  to  secure  as  hard  and  unyielding  .a  foundation  as  possible. 

Macadam's  great  objection  to  laying  down  a  bottom  of  large  stones  was  that 
such  a  foundation  acts  "  as  a  sieve  which  lets  the  water  in  which  penetrates  the 
whole  mass,  when  the  road  is  liable  to  give  way  in  all  changes  of  weather." 
Frosts  and  thaws  were  in  his  opinion  the  great  evils  to  be  guarded  against,  and 
no  made  foundation  was  equal  to  the  natural  soil  in  a  dry  state. 

There  is  no  doubt  that  little  uniformity  prevails  in  the  country.  It  may  safely 
be  said  that  most  of  the  old  roads,  if  dug  up,  would  be  found  to  have  little  or  no 
foundation,  but  many  of  those  formed  within,  say,  the  last  twenty  or  thirty  years 
would  be  found  to  rest  on  foundations  of  stones,  or  ballast,  or  some  suitable 
material  of  the  kind; 

When  a  foundation  is  used,  a  thickness  of  from  6  to  12  inches  is  recommended 
and  over  this  from  4  to  6  inches  of  metal.  But  here,  again,  no  hard  and  fast 


rule  can  be  laid  down.  The  surveyor  must  be  guided  by  circumstances — by  the 
nature  of  the  ground,  the  kind  of  material  at  his  disposal,  the  traffic,  etc. 

It  is  manifest  that  a  greater  thickness  of  foundation  should  be  given  to  a  road 
where  the  groiind  is  soft  and  the  traffic  is  of  a  heavier  nature  than  where  the 
ground  ie  hard  and  the  traffic  light.  A  less  thickness  of  good  tough  metaling 
will  suffice,  than  of  softer  material,  which  is  liable  to  break  under  pressure. 

Where  roads  are  made  without  foundation,  Macadam's  rule  will  probably  be 
found  as  correct  as  any.  He  considered  10  inches  of  metaling  sufficient  for  any 
road,  but,  in  carrying  this  out  in  practice,  it  must  never  be  forgotten  that  Mac- 
adam insisted  on  the  soil  underneath  being  perfectly  dry,  and  the  metaling,  after 
being  properly  prepared  being  thoroughly  consolidated ;  so  consolidated,  in  fact, 
as  to  prevent  any  water  passing  through  it.  It  is  this  water  getting  under  the 
surface  and  alternately  freezing  and  thawing  which  destroys  a  road  quicker 
than  anything  else. 

DRAINAGE. 

The  drainage  of  the  ground  over  which  the  road  is  to  run  is  manifestly  of  the 
very  first  importance,  because,  unless  every  precaution  is  taken  to  insure  that 
the  soil  on  which  the  road  rests  is  kept  dry  under  all  conditions  of  weather,  as 
insisted  upon  by  Macadam,  the  road  is  certain  sooner  or  later  to  be  destroyed. 

In  setting  out  the  lines  for  a  road  the  engineer  should  ascertain  very  carefully 
how  the  ground  over  which  the  road  is  to  pass  drains,  so  that  he  may  be  able  to 
make  the  best  use  of  the  natural  outfalls  of  the  country,  and  thus  get  rid  of  the 
water  from  his  road  drains  in  the  readiest  way  possible. 

Walker  particularly  recommended  that  the  side  drains  should  be  "on  the  field 
side  of  the  fence  with  apertures  in  the  fence  for  the  water  to  pass  from  the  sides 
of  the  road  into  them, "  but  this  is  by  no  means  a  rule  that  has  been  generally 
adopted,  nor  is  it  always  possible.  The  objection  to  it  is  the  difficulty  of  getting 
at  the  drains  at  every  point  to  keep  them  clear,  nor  can  the  men  in  charge  of  the 
roads  so  readily  observe  if  a  stoppage  takes  place  and  requires  to  be  removed. 

The  drains  are  in  some  places  within  the  fences  and  in  others  beyond ;  but 
wherever  the  drain  may  be  placed,  its  width  and  depth  must  evidently  be  regu- 
lated according  to  local  circumstances.  In  places  where  the  drain  after  running 
short  distances  can  relieve  itself  by  discharging  the  water  into  some  natural 
ditch  or  stream,  its  dimensions  may  be  small,  but  where  there  is  no  natural 
otatlet  for  a  long  distance  the  quantity  of  water  which  it  will  have  to  remove 
will  be  far  greater  and  its  dimensions  will  consequently  require  to  be  adjusted 
to  these  circumstances.  It  is  therefore  clear  that  in  some  places  a  drain  18  inches 
square,  or  even  smaller,  would  more  than  suffice  for  its  object,  while  in  others  a 
drain  3  feet  square,  or  larger,  would  fail  to  carry  away  the  water  flowing  into  it. 

In  some  situations,  moreover,  the  road  might  intercept  the  surface  drainage  of 
the  country,  and  provision  would  have  to  be  made  for  the  water  which  would 
naturally  flow  into  the  drain  from  the  adjacent  lands  in  addition  to  that  from 
the  road. 

In  adjusting  the  sizes  of  drains  to  roads  one  important  consideration  should 
always  be  borne  in  mind,  and  that  is  that  the  velocity  of  the  water  should  not 
be  so  great  as  to  wear  away  the  sides  and  bottom  of  the  drain.  Sewers  are  made 
as  small  as  possible  to  secure  the  greatest  velocity  and  scouring  power  with  a 
given  quantity  of  water.  The  opposite  principle  must  be  borne  in  mind  in 
designing  drains  for  roads.  The  drain  should  rather  be  made  too  large  than  too 
small,  and  too  wide  and  shallow  than  too  narrow  and  deep,  in  order  to  reduce 
the  velocity  of  the  stream,  so  that  it  shall  not  destroy  the  drain.  Deep  drains 
by  the  side  of  the  road  are  very  dangerous. 

The  level  of  the  water  in  the  drains  should  be  kept  well  below  the  material 
forming  the  road.  Macadam  considered  3  or  4  inches  sufficient,  but  others  rec- 
ommend as  mr.ch  as  a  foot  at  least,  and  more  even,  if  it  can  be  easily  obtained. 

Where  the  road  has  a  comparatively  steep  longitudinal  gradient,  and  the  water 
must  flow  with  considerable  force,  it  may  be  necessary  to  go  to  the  expense  even 
of  a  covered  drain  constructed  with  slabs  of  stone  or  stoneware  pipes  or  masonry. 

It  is  manifest  that  in  some  places  drains  would  not  be  required  on  both  sides 
of  the  road.  One  may  suffice,  but  in  these  cases  the  water  falling  on  one-half  of 
the  road  would  require  to  be  conveyed  to  the  ditch  on  the  other  side  by  drains 
laid  under  the  roadway. 

Some  surveyors  recommend  that  cross  drains  should  never  run  at  right  angles 
to  the  line  of  the  road,  but  in  a  slanting  direction.  One  advantage  of  this  is 
that  a  better  gradient  can  be  secured  for  the  drain. 


The  surveyor  should  take  great  care  that  the  line  chosen  for  the  road  does  not 
run  over  any  natural  springs  rising  to  the  surface.  Such  springs  should  be 
avoided  if  possible ;  but  in  cases  where  this  is  not  practicable,  special  means 
must  be  adopted  to  lead  off  the  water  by  drains  laid  under  the  road. 

When  there  is  a  footpath  by  the  side  of  the  road,  the  water  falling  on  that  half 
of  the  road  is  conveyed  to  the  ditch  at  regular  distances  apart  by  covered  drains 
laid  at  a  proper  inclination  under  the  path,  and  where  the  longitudinal  gradient 
of  the  road  is  so  steep  that  the  water  flowing  alongside  of  the  footpath  is  liable 
to  cut  up  the  surface,  a  proper  paved  or  other  suitable  channel  to  resist  the  action 
of  the  water  should  be  laid  down. 

Nothing  so  much  conduces  to  the  preservation  of  roads  as  good  curbs  and 
proper  side  channels  for  the  removal  of  rain,  but,  unfortunately,  curbs  are  sel- 
dom laid  except  in  towns,  and  riot  near  sufficient  attention  is  paid  to  the  con- 
struction of  side  channels,  which  are  soon  worn  into  ruts  by  the  rain. 

HEDGES  AND  FENCES. 

Air  and  sunshine  are  as  necessary  for  the  preservation  of  roads  in  good  order 
as  for  the  vigorous  health  of  plants  and  animals.  Water  and  want  of  light  are 
among  the  most  destructive  agents  in  nature,  and  no  road  can  be  kept  in  order 
which  is  always  in  a  damp  state  and  on  which  the  sun  never  shines.  Every- 
thing, therefore,  that  prevents  a  perfect  perflation  of  the  air  and  obstructs  the 
revivifying  effects  of  sunshine  is  to  be  avoided. 

Considered,  then,  from  a  purely  engineering  point  of  view,  there  is  no  doubt 
that  a  road  would  be  all  the  better  without  hedges  and  fences  of  any  kind,  but 
inasmuch  as  a  barrier  of  some  kind  or  other  between  roads  and  the  adjoining 
fields  is  absolutely  necessary  on  other  grounds,  e.  g. ,  to  keep  cattle  from  straying 
from  one  to  the  other,  to  mark  the  limits  of  property,  etc.,  a  hedge  may  be  con- 
sidered a  necessary  evil,  and  the  point,  therefore,  for  the  consideration  of  the 
engineer  is  how  to  minimize  the  evil. 

Obviously,  the  higher  and  thicker  the  hedge  the  more  obstmction  must  it 
offer  to  the  sun  and  wind.  The  object  to  be  borne  in  mind  should  be  to  erect 
such  a  barrier  as  first,  shall  allow  the  greatest  amount  of  light  and  air  to  pass 
through  it,  and  secondly,  shall  best  answer  the  nonengineering  purposes  for 
which  it  is  required. 

According  to  these  principles,  the  best  barrier  would  be  one  of  iron,  or  of  iron 
and  wood  combined,  provided  that  it  was  sufficiently  strong  to  resist  being  broken 
down  by  cattle,  horses,  etc.  Iron  wire  should  not  be  used,  as  it  is  easily  bent  out 
of  shape,  and  cattle  and  horses  are  very  apt  to  injure  themselves  in  attempting  to 
jump  over  the  fence  or  to  force  themselves  through  it.  Barbed  wire  is  still  more 
objectionable,  and  its  use,  which  is  cruelty  to  animals,  should  be  strictly  forbidden. 

A  strong  iron  fence  forms,  perhaps,  the  best  barrier,  but  it  is  costly,  and  few 
authorities  would  be  prepared  to  go  to  the. expense  of  putting  it  up,  especially  as 
it  deteriorates  with  time  and  entails  a  constant  charge  for  maintenance  in  con- 
sequence of  the  corrosion  of  the  iron  and  the  necessity  for  periodically  painting  it. 

Wood  is  not  a  suitable  material  for  a  fence,  as  it  is  easily  destroyed  by  willful 
persons  and  rots  xinder  the  effects  of  the  atmosphere ;  but,  if  used,  it  should  be 
oak  or  some  other  kind  which  resists  rot  as  long  as  possible.  Most  kinds  of 
wood  are  perfectly  useless  for  the  purpose. 

The  commonest  fence  in  England  is  the  quickset  hedge,  and  its  almost  univer- 
sal use  is  perhaps  due  to  the  fact  that  it  is  cheap  and  requires  no  skilled  labor  to 
maintain,  but  it  is  a  mistake  to  suppose  that  a  good  quickset  hedge  can  be  estab- 
lished without  care  in  planting  and  constant  subsequent  watchfulness. 

One  of  the  first  engineers  who  drew  attention  to  the  importance  of  the  subject 
of  hedges  in  connection  with  roads  was  John  Walker,  who  in  his  evidence  before 
Parliament  said : 

"  The  fences  on  each  side  form  a  very  material  and  important  subject  with  re- 
gard to  the  perfection  of  roads ;  they  should  in  no  instance  be  more  than  5  feet  in 
height  above  the  center  of  the  road,  and  all  trees  which  stand  within  20  yards 
of  it  ought  to  be  removed.  I  am  sure  that  20  per  cent  of  the  expense  of 
improving  and  repairing  roads  is  incurred  by  the  improper  state  of  the  fences 
and  trees  along  the  side  of  it,  on  the  sunny  side  more  particularly.  This  must 
be  evident  to  any  person  who  will  notice  the  state  of  a  road  which  is  much 
shaded  by  high  fences  and  trees,  compared  to  the  other  parts  of  the  road  which 
are  exposed  to  the  sun  and  air.  My  observations  with  regard  to  fences  and  trees 
apply  when  the  road  is  on  the  same  level  as  the  adjacent  field ;  but  in  many  cases 
on  the  most  frequented  roads  in  England  more  stuff  has  been  removed  from  time 


to  time  than  was  put  on ;  the  snrf ace  of  the  road  is  consequently  sunk  into  a 
trough  or  channel  from  3  to  6  feet  below  the  surface  of  the  fields  on  each  side. 
Here  all  attempts  at  drainage  or  even  common  repairs  seem  to  be  quite  out  of 
the  question ;  and  by  much  the  most  judicious  and  economical  mode  will  be  to 
remove  the  whole  road  into  the  field  which  is  on  the  sunny  side  of  it." 

Mr.  Law  in  his  work  on  "Roads "  makes  some  very  useful  observations: 

"Few  persons  are  aware  of  the  extent  to  which  a  road  may  be  injured  by  high 
hedges  or  lines  of  trees.  Trees  are  worse  than  hedges,  because  they  not  only 
deprive  the  road  of  the  action  of  the  air  and  sun,  but  they  further  injure  it  by 
the  dripping  of  rain  from  their  leaves,  as  a  consequence  of  which  the  road  is  kept 
in  a  wet  state  long  after  it  would  otherwise  have  become  dry. 

' '  When  fences  are  indispensable  they  should  be  placed  as  far  as  may  be  from 
the  sides  of  the  road,  and  should  be  kept  as  low  as  possible.  When  there  is  a 
deep  ditch  on  either  side  of  the  road  it  becomes  necessary,  to  prevent  accident, 
that  the  fence  should  be  placed  between  the  road  and  the  ditch,  but  in  other 
situations  the  fence  should  be  placed  on  the  field  side  of  the  ditch.  In  so  doing 
the  surface  draining  of  the  road  into  the  side  ditches  is  less  interferred  with  and 
the  action  of  air  and  sunshine  is  less  obstructed  by  the  fence. 

' '  The  different  descriptions  of  fence  which  may  be  employed  are  various.  In 
districts  where  stone  is  plentiful,  and  especially  in  the  immediate  neighborhood 
of  quarries,  where  stone  rubble  can  be  obtained  at  a  trifling  cost,  dry  rubble  walls, 
without  any  mortar,  are  very  good  and  cheap  and  require  little  or  no  repair. 

"For  the  road  itself,  an  open  post-and-rail  fence  is  the  best  which  can  be  em- 
ployed, because  it  scarcely  impedes  the  action  of  the  wind  and  the  sun  upon  the 
surface  of  the  road,  but  the  great  practical  objection  to  timber  fences  is  their 
liability  to  decay,  which  occasions  freqent  and  constant  expense  for  renewal. 

"  The  most  common,  and,  all  things  considered,  the  most  useful  fence  is  the 
quickset  hedge.  If  properly  planted  and  carefully  attended  to  for  the  first  few 
years,  a  natural  fence  may  be  obtained  sufficiently  strong  to  resist  the  efforts  of 
cattle  to  break  through,  and  very  economical  in  cost  for  maintenance.  A  bank 
or  mound  of  earth  at  least  2  feet  in  depth  should  be  prepared  for  the  reception  of 
the  quicks,  which  should  be  three  years'  plants  which  have  been  transplanted 
two  years.  The  best  kind  of  soil  is  one  of  a  light  sandy  nature,  admitting  suffi- 
cient moisture  to  nourish  the  plants  and  retaining  moisture  in  dry  seasons. 
Heavy  clay  soils  are  not  sufficiently  pervious  to  water,  and  plants  placed  in  such 
soils  are  never  found  to  thrive.  A  mixture  of  peat  or  of  rotten  leaves  is  of  great 
use  and  causes  the  plants  to  grow  with  much  vigor.  The  quicks  are  most  com- 
monly planted  in  a  single  row,  at  distances  of  about  4  inches  apart.  But  a 
much  better  hedge  is  formed  by  planting  them  6  inches  apart  in  a  double  row, 
as  shown  below,  with  a  space  6  inches  between  the  rows, 

OOOOOOOOO 


and  so  arranged  that  the  plants  in  one  row  are  opposite  the  spaces  in  the  other. 
By  this  arrangement,  although  the  plants  are  really  not  so  crowded,  and  have 
more  space  around  their  roots  from  which  to  derive  nourishment  than  in  a  single 
row,  they  form  a  thicker  hedge.  The  proper  time  for  planting  quicks  is  during 
the  autumn  or  the  spring,  and,  in  fine  seasons,  the  operation  may  be  continued 
during  the  whole  winter.  A  temporary  fence  should  be  put  up  to  protect  the 
young  plants  from  injury,  and  the  fence  should  be  retained  until  the  hedge  has 
attained  sufficient  strength  to  require  its  protection  no  longer— a  period,  under 
favorable  circumstances,  of  three  or  four  years  after  the  quicks  are  planted. 
That  the  plants  may  thrive  they  must  be  carefully  attended  to  at  first,  and  it  is 
essential  that  they  should  be  properly  cleaned  and  weeded  at  least  twice  every 
year.  Once  every  year,  toward  the  end  of  the  summer,  the  hedge  should  be  ju 
diciously  trimmed,  not  to  such  an  extent  as  to  produce  stunted  plants,  but  by 
merely  cutting  off  the  upper  and  more  straggling  shoots,  so  as  to  bring  it  to  a 
level  and  even  surface.  By  proceeding  in  this  manner,  a  neat,  strong,  and  com- 
pact hedge  of  healthy  plants  will  be  obtained  in  about  three  years  after  planting. " 
Trees,  however  much  they  may  add  to  the  picturesqueness  of  a  road,  add  still 
more  to  the  difficulty  of  keeping  it  in  repair  ;  and  thick  avenues,  i.  e.,  trees 
planted  close  to  each  other  on  both  sides  of  a  road,  are  quite  incompatible  with 
the  due  preservation  of  the  surface.  The  evil  is  worse  the  narrower  the  road  is, 
for  then  very  little  sunshine  can  get  to  the  road  at  all,  so  that  the  macadam  is 
constantly  damp  and  wears  away  much  more  rapidly  under  traffic/ 


8 

What  are  understood  as  boulevards  are  not  so  objectionable,  because  the  roads 
are  usually  very  wide  and  the  trees  are  not  planted  so  close  as  in  an  avenue,  but 
from  an  engineering  point  of  view,  everything  that  interferes  with  the  sun  and 
prevents  the  circulation  of  air  is  objectionable. 


It  is  to  the  use  of  broken  stone  for  the  formation  of  roads  to  which,  more  than 
anything  else,  we  owe  the  great  improvement  in  the  roadways  of  this  country. 
It  is  not  quite  clear  who  really  discovered  the  virtues  of  hard  stones  broken 
into  small,  angular  pieces,  but  John  London  Macadam  has  probably  a  better 
claim  to  the  title  of  discoverer  than  anyone  else.  He  it  was,  at  all  events,  who 
explained  the  principles  of  the  use  of  macadam,  the  size  to  which  stone  should 
be  broken,  the  manner  in  which  it  should  be  laid,  and  so  forth;  and  thus  it  is 
that  the  kind  of  road  he  introduced  has  ever  since  borne  his  name,  not  only  in 
England  but  in  many  foreign  countries. 

Macadam  attached  the  greatest  importance  to  the  size  to  which  stone  should 
be  broken.  He  said : 

"The  size  of  stone  used  on  a  road  must  be  in  due  proportion  to  the  space 
occupied  by  a  wheel  of  ordinary  dimensions  on  a  smooth,  level  surface.  This 
point  of  contact  will  be  found  to  be,  longitudinally,  about  an  inch,  and  every 
piece  of  stone  put  into  a  road  which  exceeds  an  inch  in  any  of  its  dimensions  is 
mischievous." 

But  he  thought  it  a  better  plan  to  specify  the  size,  not  by  its  dimensions,  but 
by  its  weight,  and  he  fixed  6  ounces  as  the  proper  maximum  weight  of  each 
piece.  His  reasoning  was  that  by  expei'inient  he  had  found  very  little  difference 
in  the  sizes  of  different  kinds  of  stone  broken  to  this  weight,  however  much  the 
stone  might  vary  in  specific  gravity. 

He  said:  "  I  hold  six  ounces  to  be  the  maximum  size.  If  you  made  the  road 
of  all  six-ounce  stones  it  would  be  a  rough  road ;  but  it  is  impossible  but  that 
the  greater  part  of  the  stones  must  be  under  that  size." 

Whether  Macadam  was  right  or  wrong,  the  principle  he  laid  down  has  not 
been  adopted  in  this  country.  Nowhere  is  the  size  of  macadam  regulated  by 
weight,  but  invariably  by  dimensions.  It  is  propable  that  the  inconvenience  of 
having  to  weigh  stones  in  a  balance  to  be  carried  about  by  the  surveyor  compared 
with  the  rapidity  with  which  they  can  be  measured  by  means  of  a  gauge,  has 
caus-ed  the  former  practice  to  be  abandoned.  Broken  stone  to  be  used  for  a  road 
is  now  generally  specified  to  be  of  a  size  so  that  it  shall  just  pass  in  any  direc- 
tion through  a  gauge  of  certain  dimensions. 

Considerable  importance  is  attached  to  the  manner  in  which  macadam  is  pre- 
pared for  use.  Machine -broken  stone  is  not  considered  of  the  same  value  as  that 
broken  by  hand.  The  stones  are  not  of  so  regular  a  size  and  shape,  and  there  is  a 
greater  proportion  of  inferior  stuff.  A  mechanical  crusher  is  apt  to  stun  the 
material  and  does  not  leave  the  edges  so  sharp  for  binding  as  they  are  when  the 
stone  is  broken  with  a  small  hammer. 

It  is  probable  that  the  crusher  by  its  severe  blows  affects  the  interior  constitu- 
tion of  the  stone  and  renders  the  fragments  more  liable  to  split  under  the  roller. 

Macadam,  who  never  thought  anything  regarding  road -making  beneath  his 
notice,  laid  it  down  that  stone  should  only  be  broken  by  people  sitting  on  their 
haunches  and  striking  it  with  a  small  hammer.  This  serves  just  to  break  the 
stone  and  no  more.  The  edges  are  sharp  and  the  fragments,  not  having  received 
too  great  a  blow  to  affect  the  internal  structure  of  the  stone,  remain  thoroughly 
sound  and  are  tough  enough  to  resist  the  crushing  power  of  the  roller.  It  should 
be  borne  in  mind,  however,  that  in  Macadam's  time  mechanical  stone -crushers 
were  not  in  existence,  nor  even  were  road  rollers  in  regular  use,  although  they 
had  been  invented. 

Taking  all  these  points  into  consideration,  it  is  probable  that  the  best  size  for 
macadam  for  hard  and  tough  stones,  such  as  basalt,  close-grained  granite,  syenite, 
gneiss,  and  the  hardest  of  the  primary  crystallized  rocks,  is  from  1£  to  If  inches 
cube,  according  to  their  respective  toughness  and  hardness,  while  stone  of  me- 
dium quality  ought  to  be  broken  to  gauge  of  from  H  to  2£  inches,  and  the  softer 
kinds  of  stone  might  vary  between  the  limits  of  2  and  2£  or  2£  inches,  but  the 
latter  is  a  size  which  should  seldom  be  specified. 

As  in  everything  else  in  connection  with  roads,  no  hard  and  fast  line  can  be 
drawn,  but  the  surveyor  must  prescribe  the  size  to  which  macadam  should  be 
broken  according  to  his  knowledge  of  the  properties  of  the  stone  he  proposes  to 
use.  Stones  which  bear  even  the  same  name  are  often  as  different  in  their  prop- 
erties as  possible. 


The  present  writer  is  opposed  to  the  use  of  large  macadam.  Where  the  sur- 
veyor has  only  a  comparatively  soft  stone  to  form  his  roads  with,  the  better 
plan  in  his  opinion  is  to  break  the  stone  to  2  or  2±  inches  gauge,  but  in  putting 
it  down  in  any  quantity  to  roll  it  at  first  with  a  light  roller  till  the  stones  are 
fitted  into  their  places  and  have  become  well  consolidated.  The  passage  of  a 
heavy  roller  afterwards  will  not  then  be  so  apt  to  crush  the  material.  Unfortu- 
nately most  surveyors  are  so  enamored  of  heavy  rollers  that  very  few  are  aware 
of  the  advantages  to  be  derived  from  the  judicious  use  of  light  ones,  which  are 
seldom  to  be  found  in  the  country. 

ROLLERS  AND  ROLLING 

The  proper  method  of  rolling  macadam  and  the  best  weight  for  rollers  are  very 
important  questions  in  the  formation  and  repair  of  roads.  It  does  not  at  all  fol- 
low that  the  best  weight  for  a  roller  for  one  county  or  country  is  the  best  for  all. 
In  a  district  where  the  only  materials  to  be  had  are  more  or  less  of  a  soft  nature  a 
much  lighter  roller  is  necessary  than  in  one  where  the  toughest  basalts,  granites, 
etc.,  are  used.  Heavy  rollers  would  crush  the  soft  materials  to  powder  and  so 
destroy  them  for  all  practical  purposes.  Such  rollers,  moreover,  are  quite  unsuit- 
able for  roads  under  which  there  are  water  and  gas  pipes  laid  at  a  sufficient 
depth  beneath  the  surface  to  resist  the  crushing  power  of  a  heavy  load.  The 
penalty  to  be  paid  for  destroying  a  water  or  gas  pipe  is  too  serious  to  be  lightly 
incurred,  and  before-  deciding  on  the  weight  for  his  roller,  the  surveyor  should 
be  careful  to  ascertain  the  positions  and  sizes  of  all  the  pipes  imder  the  roads  in 
his  district,  together  with  the  depths  below  the  surfaces  at  which  the  pipes  have 
been  laid,  or  he  may  do  much  mischief  before  he  becomes  aware  of  it. 

The  present  writer  is  of  opinion  that  the  use  of  heavy  rollers,  which  has  been 
growing  of  late,  is  a  mistake,  and  is  only  to  be  justified  in  towns  where  it  is  de- 
sirable to  finish  roads  as  soon  as  possible,  so  that  there  shall  be  the  minimum  of 
interruption  to  traffic.  The  heavier  the  roller,  the  more  liable  is  the  material  to 
be  crushed  under  the  load,  so  that,  unless  the  very  best  material  is  used,  a  15-ton 
roller  is  much  too  heavy  for  the  object  in  view — most  certainly  for  the  general 
purposes  of  the  surveyor  in  a  county  district. 

When  the  materials  used  in  a  district  are  of  different  kinds,  i.  e.,  when  gran- 
ites, syenites,  basalts,  etc.,  are  used  for  the  best  roads,  and  inferior  stone  for  the 
minor  ones,  it  is  essential  that  there  should  be  two  rollers — one  of  a  heavier,  and 
the  other  of  a  lighter  kind,  each  to  be  used  on  the  materials  suited  to  it. 

The  present  writer  is  of  opinion  that  a  road  formed  with  a  light  roller,  although 
it  can  not  be  made  to  consolidate  so  soon,  lasts  longer  than  one  formed  with  a 
heavier  roller.  The  consolidation  in  the  latter  case  is  effected  more  rapidly,  but 
at  the  sacrifice  of  much  of  the  stone  being  broken  or  crushed  into  position.  The 
lighter  roller  effects  a  truer  binding  of  the  macadam  without  breaking  the  stones 
into  smaller  fragments. 

Even  when  the  best  and  toughest  materials  are  used,  it  will  be  found  advanta- 
geous to  begin  the  rolling  with  a  light  roller,  and  only  finish  with  a  heavier  one. 

In  rolling  fresh  material  the  use  of  the  light  roller  shoiild  be  continued  until 
it  is  observed  that  none  of  the  stones  advance  from  their  positions,  when  the 
heavier  roller  should  be  brought  onto  the  work,  and  its  use  continued  Tintil 
again  it  is  found  that  no  shifting  of  the  macadam  takes  place. 

MAKING  A  ROAD. 

After  the  land  over  which  the  road  is  run  has  been  properly  drained  and  fenced 
in,  the  surface  of  the  ground  should  be  leveled,  or,  rather,  brought  to  the  form 
of  the  curve  of  the.  road,  and  all  soft  and  boggy  soil  rectified,  either  by  its  re- 
moval and  replacement  with  sound,  hard  material,  or  in  some  other  way.  Some 
surveyors  recommend  the  use  of  faggots  and  brushwood,  which,  if  used,  should 
be  laid  down  in  fascines  or  bundles,  one  layer  over  the  other  and  crosswise ;  but 
others  consider  the  use  of  such  material  for  raising  a  road  very  objectionable, 
unless  the  brushwood  is  always  in  water.  If  it  is  alternately  wet  and  dry,  it  rots, 
and  its  destruction  soon  follows,  causing  the  road  to  sink. 

The  present  writer  is  altogether  opposed  to  the  use  of  brushwood  except  across 
a  morass,  where  it  may  be  considered  to  serve  the  same  object  as  that  of  pontoons 
across  a  river— i.  e.,  to  support  the  road  and  prevent  its  sinking  through  the  bog. 

Some  surveyors  recommend  that  the  surface  soil  should  be  removed,  while 
others  prefer  not  to  disturb  it.  Here,  again,  common  sense  must  dictate  the  proper 
course  to  be  pursued.  If  the  surface  soil  is  suitable  for  a  foundation  and  superior  to 
that  on  which  it  rests,  it  should  be  retained ;  but  if  otherwise,  it  should  be  removed, 
so  as  to  give  the  road  the  best  foundation  possible— i.  e.,  the  driest  and  firmest. 


10 

When  all  the  soft  and  defective  places  have  been  excavated  and  refilled  Avith 
good  material,  and  the  entire  surface  has  been  brought  to  the  proper  curve,  the 
road  should  be  well  rolled  with  a  light  roller,  and  materials  should  be  added  in 
the  soft  places  as  these  sink  from  time  to  time.  The  rolling  should  be  continued 
until  no  more  sinking  takes  place  in  any  part  of  the  road,  when  the  light  roller 
should  be  taken  off  and  a  heavy  one  substituted  in  its  place,  the  soft  places  again 
being  made  good  with  good  material  as  they  sink.  When  all  sinking  has  ceased 
the  surface  soil  may  be  considered  fit  to  receive  the  foundation. 

Where  the  soil  is  very  soft,  it  will  often  be  found  impossible  to  use  a  roller  at 
all,  in  which  case  the  foundation  must  be  put  down  before  the  rolling  begins. 

This  foundation  is  formed  in  various  ways,  and,  of  course,  with  such  materials 
as  can  be  obtained  in  the  district.  When  stones  of  a  rather  large  size  are  used, 
they  should  be,  as  recommended  by  Telford  and  so  many  of  the  surveyors,  hand- 
pitched  with  their  broadest  side  downward,  so  as  to  insure  them  bedding  properly, 
and  the  interstices  should  be  filled  with  smaller  stones.  Then  a  layer  of  2  or  :' 
inches  of  macadam  should  be  put  down  and  a  thin  sprinkling  of  some  binding 
material  should  be  thrown  over  the  macadam.  The  road  should  then  be  well 
watered  and  rolled.  When  this  has  been  thoroughly  well  consolidated  the  second 
layer  of  macadam,  about  8  inches  thick,  with  some  binding  material,  if  the  stone 
is  too  clean,  should  be  put  down ;  when  this  has  been  well  rolled  and  has  become 
consolidated,  carriages  may  be  allowed  to  pass  over  the  road. 

The  materials  used  for  foundations  are  of  very  different  kinds,  many  being 
quite  unsuited  for  the  purpose ;  large  stones  of  almost  any  sort,  furnace  slag  and 
clinkers,  ballast,  flints,  chalk,  broken  pottery,  tin  cans — any  material  indeed  that 
can  be  found  ready  to  hand. 

The  use  of  soft  material  in  a  foundation  should  be  avoided  if  possible,  as  the 
effect  of  rolling  the  road  will  be  to  crush  the  material  to  powder,  and  this  is  the 
state  to  which  such  foundation  must  inevitably  be  reduced  by  the  traffic  in  the 
course  of  time. 

It  is  almost  the  universal  practice  now  to  sprinkle  some  binding  material  over 
the  macadam  before  rolling  it.  This  is  usually  gravel  or  sand  or  chalk  or  clip- 
pings from  quarries.  It  is  a  practice,  however,  which  Macadam  condemned 
with  all  the  force  of  his  character.  His  opinion  was  that  any  material  like  sand, 
or  fine  gravel  or  chalk,  allowed  rain  to  pass  through  to  the  bottom,  whereas,  by 
rolling  the  macadam  without  the  use  of  any  binding  material,  the  mass  became 
so  consolidated  as  to  offer  an  impenetrable  barrier  to  the  passage  of  the  water. 

The  views  expressed  by  Mr.  Law,  C.  E.,  in  his  "The  Art  of  Constructing  Com 
mon  Roads,"  on  this  subject,  are  worthy  of  much  considei'ation.  He  says: 

' '  If  the  materials  of  which  the  covering  is  to  be  formed  are  in  angular  masses 
no  binding  of  any  description  is  requisite,  as  they  quickly  become  united  by  dove- 
tailing, as  it  were,  amongst  each  other  much  more  firmly  than  they  would  by 
the  use  of  any  kind  of  artificial  cement. 

"When  the  stones  instead  of  being  angular  are  round  and  pebly,  like  gravel 
stones,  it  is  necessary  to  mix  them  with  just  sufficient  foreign  matter  of  binding 
nature  as  will  serve  to  fill  up  the  interstices  between  the  stones,  for  otherwise 
these  would  roll  about  and  prevent  the  road  from  becoming  solid. 

' '  There  are  then  two  methods  of  cementing  or  solidifying  the  surface  of  a 
road— one  by  the  mechanical  form  of  the  materials  themselves,  forming  a  species 
of  bond;  the  other,  by  the  use  of  some  cementing  or  binding  matter.  And  in 
comparing  the  relative  merits  of  the  two,  the  preference  must  certainly  be  given 
to  the  former — that  in  which  the  stones  are  united  by  virtue  of  their  angular 
form  without  the  use  of  any  cementing  material.  The  principal  reason  for  this 
preference  is  that  roads  formed  with  stones  so  united  are  not  materially  affected 
by  wet  or  frosty  weather,  whereas  roads  whose  surfaces  are'  composed  of  pebbly 
stones  united  by  cementing  material  become  loose  and  rotten  under  such  cir- 
cumstances, the  cementing  material  becoming  softened  by  the  wet  and  reduced 
to  a  loose,  pulverulent  condition  by  subsequent  frost." 

Mr.  Law  reasons  on  the  subject  exactly  as  Macadam  did,  whose  views  the 
present  writer  indorses. 

Some  surveyors  are  of  opinion  that,  in  laying  down  macadam,  it  should  be 
sorted  into  two  or  three  different  kinds,  with  a  view  to  the  larger-sized  ma- 
terial being  placed  at  the  bottom  and  the  smaller  at  the  top.  This  is  not  recom 
mended  by  the  present  writer. 

When  the  surveyors  have  expressed  any  opinion  on  the  subject  they  seem  to 
be  nearly  all  agreed  that  the  bottom  of  the  road  should  not  be  leveled,  but 
formed  to  the  curve  of  the  surface  of  the  road,  as  it  is  to  be  when  completed. 
When  the  natural  ground  on  which  the  road  rests  is  clay,  or  other  impervious 


11 

soil,  it  is  clear  that  to  make  the  bottom  of  the  road  flat,  is  to  induce  the  water 
percolating  through  the  macadam  and  foundation  to  rest  in  hollows  below, 
whereas,  if  the  bottom  is  curved,  the  water  is  more  likely  to  flow  off  to  the  sides, 
and  thus  to  leave  the  foundation  and  macadam  dry.  Moreover,  as  the  wear  of 
the  road  should  be  the  same  in  all  parts,  the  thickness  of  the  material  should 
likewise  be  the  same  everywhere. 

REPAIR   OF  ROADS. 

As  in  the  making  and  maintenance  of  roads,  it  is  essential  that  there  should 
be  abundance  of  water,  without  the  use  of  which  the  surface  can  not  be  easily 
broken  up,  nor  the  macadam  be  got  to  consolidate  properly,  the  best  season  for 
doing  work  of  this  nature  is  that  part  of  the  year  when  water  is  plentiful  and 
can  be  easily  got,  and  when  the  roads  are  softened  with  rain  or  moisture,  i.  e., 
the  late  months  of  autumn  and  early  winter. 

It  is  not  considered  a  good  plan  to  coat  a  long  length  of  road  with  material 
at  once,  because,  if  this  is  done,  vehicles  avoid  going  over  the  macadam,  and 
thus  prevent  it  from  consolidating  quickly.  If  short  lengths  only  of  the  road 
are  put  under  repair,  the  drivers  find  it  more  troublesome  to  be  constantly 
avoiding  them  than  to  keep  straight  on  their  course,  and  thus  the  material  is 
got  to  bind  much  sooner. 

After  April  and  in  summer,  or  the  dry  months  of  the  year,  all  loose  stones 
should  be  removed  from  the  road,  for,  if  allowed  to  remain,  wheels  passing  over 
them  loosen  the  material  on  which  those  stones  rest,  and  thus  cause  much 
damage  to  the  surface  of  the  road. 

The  proper  maintenance  of  a  road  consists  in  keeping  the  surface  always 
.smooth  for  traffic  and  in  taking  care  that  the  thickness  of  the  macadam  is  not 
unduly  diminished  by  wear.  A  road  may  be  smooth  on  the  surface,  but,  if  the 
material  is  nearly  worn  away,  it  can  not  be  considered  to  have  been  properly 
maintained.  To  keep  a  road  in  an  efficient  manner  unceasing  vigilance  is 
required.  Ruts  and  hollows  should  be  at  once  filled  in  with  macadam,  and  all 
weak  places  as  soon  as  observed  treated  similarly. 

A  common  fault  is  to  put  too  great  a  thickness  of  stone  down  at  once.  Pen- 
fold  says : 

"  It  is  one  of  the  greatest  mistakes  in  roadmaking  that  can  be  committed  to 
lay  on  thick  coats  of  materials,  and  when  understood  it  will  no  longer  be 
resorted  to.  If  there  be  substance  enough  already  in  the  road,  which,  indeed, 
should  always  be  carefully  kept  up,  it  will  never  be  right  to  put  on  more  than  a 
stone's  thickness  at  a  time.  A  cubic  yard,  nicely  prepared  and  broken  to  a 
rod  superficial  will  be  quite  enough  for  a  coat,  and  will  be  found  to  last  as  long 
as  double  the  quantity  put  on  unprepared  and  in  thick  layers.  There  is  no 
grinding  to  pieces  when  so  applied ;  the  angles  are  preserved  and  the  material  is 
out  of  sight  and  incorporated  in  a  very  little  time.  Each  stone  becomes  fixed 
directly  and  keeps  its  place,  thereby  escaping  the  wear  and  fretting  which 
occur  in  the  other  case." 

For  repairs  of  this  nature,  where,  in  fact,  the  mere  surface  of  the  road  only 
is  sought  to  be  put  in  order,  no  binding  material  is  used  or  necessary.  The 
wheels  of  the  carriages  gradually  push  the  stones  into  their  places,  and  make 
them  bind  with  the  old  material  on  the  road.  Some  engineers  are  of  opinion 
that  no  macadam  should  be  laid  down,  however  thin  the  coating  may  be,  with 
out  the  surface  of  the  road  being  roughened  with  a  pick.  There  is  no  doubt  that 
this  tends  to  make  the  new  material  bind  with  the  old  much  sooner,  but,  on  the 
other  hand,  it  tends  to  disturb  and  to  weaken  the  crust  if  it  should  be  very  thin. 

For  more  extensive  repairs,  i.  e.,  when  a  road  has  been  allowed  to  become 
very  thin,  and  it  is  necessary  that  a  considerable  thickness  of  material  should 
be  laid  on,  the  road  must  be  what  Macadam  termed  "lifted,"  or  broken  with  a 
pick  to  the  depth  of  2  or  3  inches,  and  all  large  stones  must  be  thrown  aside  to 
be  broken  to  the  required  dimension.  A  thin  layer  of  new  macadam  must  now 
be  added  and  the  road  rolled.  It  will  usually  be  found  that  no  binding  material 
will  be  necessary.  When  this  layer  has  become  consolidated,  another,  2  or  3 
inches  thick,  should  be  laid  down  and  again  rolled,  and  so  on  until  the  desired 
thickness  of  material  for  the  road  has  been  obtained. 

Macadam  objected  to  the  use  of  any  binding  material,  such  as  gravel,  sand, 
chalk,  etc. ,  being  used  with  the  view  to  help  the  macadam  to  bind,  but  the 
almost  universal  practice  now  is  to  sprinkle  some  such  material  over  the 
macadam  before  rolling  it. 


12 

The  present  writer's  views  accord  with  those  of  Macadam.  In  his  opinion  the 
bad  state  of  many  of  the  roads  in  the  country  and  the  constant  repairs  required 
to  them,  are  in  great  part  the  result  of  the  use  of  binding  materials,  which  being 
invariably  of  a  pervious  nature,  afford  the  rain  innumerable  passages  through 
the  macadam  to  the  foundation  underneath.  Thus,  not  only  is  there  water 
below  the  road,  but  the  macadam  and  foundation  are  so  thoroughly  saturated 
with  wet  that  no  power  on  earth  can  possibly  resist  the  loosening,  disintegrating 
and  destroying  effect  of  a  few  alternations  of  frosts  and  thaws. 

No  road  should  be  lifted  unless  it  has  been  softened  with  rain,  and  there  is 
plenty  of  water  to  finish  the  work  of  reformation.  To  lift  and  remake  a  road  in 
dry  summer  weather  should  not  be  attempted.  The  work  should  be  deferred  to 
the  later  months  of  the  year,  but  not  too  late,  lest  frosts  should  set  in.  Some 
engineers  consider  October  the  best  month  in  the  year  for  lifting  a  road,  so  that 
the  material  may  be  sifted  and  sorted  when  dry,  and  be  consolidated  in  Novem- 
ber and  December, 

It  is,  indeed,  of  great  importance  to  avoid  all  extensive  work  on  a  road  if  there 
is  any  likelihood  of  frost,  for  the  effect  of  a  frost  and  then  a  subsequent  thaw  on 
macadam  recently  laid  after  it  has  been  well  watered  and  has  just  become  con- 
solidated, but  is  still  saturated  with  rain,  is  not  only  to  loosen  it,  but  also  to 
disintegrate  the  material. 

Macadam  thought  that  a  road  which  had  a  sufficient  thickness  of  stone  but 
was  out  of  order  should  not  be  repaired  with  new  material,  but  by  picking  up 
the  old  stone  and  reforming  the  road  with  it. 

He  said : 

' '  No  addition  of  materials  is  to  be  brought  upon  a  road  unless,  in  any  part  of 
it,  it  be  found  that  there  is  not  a  quantity  of  clean  stone  equal  to  10  inches  in 
thickness. 

' '  The  stone  already  in  the  road  is  to  be  loosened  and  broken  up,  so  that  no 
piece  shall  exceed  6  ounces  in  weight. 

"  The  road  is  then  to  be  laid  as  flat  as  possible.  A  rise  of  3  inches  from  the 
center  to  the  side  is  sufficient  for  a  road  30  feet  wide. 

"  The  stones  when  loosened  in  the  road  are  to  be  gathered  off  by  means  of  ;i 
strong,  heavy  rake,  with  teeth  2£  inches  in  length,  to  the  side  of  the  road  and 
there  broken,  and  on  no  account  are  stones  to  be  broken  on  the  road. 

' '  When  the  great  stones  have  been  removed  and  none  left  in  the  road  exceed 
ing  6  ounces,  the  road  is  to  be  put  in  shape  and  a  rake  employed  to  smooth  the  sur 
face,  which  will  at  the  same  time  bring  to  the  surface  the  remaining  stone  and 
will  allow  the  dirt  to  go  down. 

' '  When  the  road  is  so  prepared,  the  stone  that  has  been  broken  by  the  side  of 
the  road  is  then  to  be  carefully  spread  over  on  it.  This  is  rather  a  nice  operation 
and  the  future  quality  of  the  road  will  greatly  depend  on  the  manner  in  which 
it  is  performed.  The  stone  must  not  be  laid  on  in  shovelfuls,  but  scattered  over 
the  surface,  one  shovel  following  another  and  spreading  over  a  considerable 
space." 

A  little  new  macadam,  however,  mixed  with  the  old,  will  considerably  im- 
prove the  surface  of  the  road.  The  old  material  lifted  with  a  pick,  even  if 
broken  afresh,  never  has  the  sharp  edges  of  new  macadam,  and  much  of  it  is  too 
rounded  to  bind  in  the  same  effective  manner  as  freshly -broken  stone.  More 
over,  a  great  portion  of  the  old  macadam  when  lifted  will  be  found  to  consist  of 
material  which  has  been  reduced  either  to  dust  or  to  too  small  a  size  to  be  fit  for 
subsequent  use.  This  material  ought  to  be  rejected,  or,  if  used,  it  should  only 
be  employed  for  binding  purposes. 


